Deformable pouches for zonal isolation

ABSTRACT

A method for plugging or sealing voids in a formation may include introducing deformable pouches enclosing solid particulate materials into a fluid being pumped down the well; and injecting the deformable pouches into the voids of the formation; wherein at least one dimension of the deformable pouches may be between about 1 mm and 100 mm.

BACKGROUND

Treatments of horizontal oil and gas wells as well as vertical or declined wells in multi-layered formations frequently require using diverting techniques in order to enable the redirection of applied treatments between different zones. Some commonly used diverting methods include, but are not limited to, using mechanical isolation devices such as packers and wellbore plugs, setting bridge plugs, pumping wellbore fluids containing ball sealers, or pumping wellbore fluids containing blends of particles with fibers/flakes.

The use of wellbore fluids containing ball sealers for treatment diversion includes introducing ball-shaped sealers into the well, where they are delivered by the pumping fluid to the perforation holes in the casing where they become lodged or seated. Once seated, a ball sealer prevents the fluid penetration from the wellbore into the zone behind casing. That blockage increases pressure in the wellbore and enables the redirection of applied treatments to another unblocked zone(s) where no or little stimulation activity has happened. Although ball sealers provide efficient and cost-effective solution there are still some problems with their sealing and seating effectiveness. For example, the deviation of actual geometry of the perforation entry from the shape of an ideal circle may lead to incomplete stopping of wellbore fluid penetration into the sealed zone. Another problem can be the early release of the ball sealers from the perforations, often due to a temporary reduction of wellbore pressure during a treatment, resulting in the unintended opening of the sealed zone.

Using particulate materials (e.g., particle blends and/or fibers/flakes) for treatment diversion is based on the bridging of the particulates in narrow voids behind the casing, typically in fractures or wormholes within the formation, with subsequent accumulation of particles on the created bridge to form a plug within the void/fracture. However, it is difficult to predict the distance from the wellbore where particles will eventually bridge, making it difficult to estimate the volume of particulate materials required for successful diversion. Further, there can be a reduced bridging ability of the diverting particulate slurry during pumping because of its dilution with wellbore fluid during the pumping downhole (interface mixing). Additionally, when using a blend of particles of different sizes a higher than expected permeability of the formed plugs is often observed because of the separation of particles during pumping into groups of particles of specific sizes. FIG. 1 depicts a graphical representation (not to scale) of how an initially homogenously blended particulate slurry 10 can become a size-segmented fluid 12 during pumping downhole. The size-segmentation effect may be more noticeable when the pumping of the particle blend occurs over longer wellbore lengths in order to arrive at the void/fracture needing to be plugged for treatment diversion.

SUMMARY

In one aspect, embodiments disclosed herein relate to a method for plugging or sealing voids in a formation that includes introducing deformable pouches enclosing solid particulate materials into a fluid being pumped down the well; and injecting the deformable pouches into the voids of the formation; wherein at least one dimension of the deformable pouches may be between about 1 mm and 100 mm.

In another aspect, embodiments disclosed herein relate to a method for fracturing a wellbore that includes perforating a wellbore casing to form a perforation cluster in a first zone of a wellbore casing; subjecting the perforation cluster in the first zone to a fracturing treatment; pumping a fluid including deformable pouches downhole; and injecting the deformable pouches into voids in the formation behind the first zone of the wellbore casing.

In yet another aspect, embodiments disclosed herein relate to a method for plugging or sealing voids in a formation that includes introducing deformable pouches enclosing solid particulate materials into a fluid being pumped down the well; and injecting the deformable pouches into the voids of the formation located behind the wellbore casing; wherein at least one dimension of the deformable pouches may be between about 1 mm and 100 mm; and wherein the deformable pouches are partially or completely destroyable in the downhole environment.

In yet another aspect, embodiments disclosed herein relate to a method for plugging or sealing voids in a formation that includes introducing deformable pouches enclosing solid particulate materials into a fluid being pumped down the well; and packing the deformable pouches into the voids of the formation; wherein at least one dimension of the deformable pouches may be between about 1 mm and 100 mm; and wherein the deformable pouches are substantially stable in the downhole environment.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a graphical representation of the size-segmentation of a blended particulate slurry during pumping downhole.

FIG. 2 shows an illustration of a use of deformable pouches according to an embodiment of the present disclosure.

FIG. 3 shows a schematic of a modified flow injector.

FIG. 4 depicts a flow chart for a multi-stage hydraulic fracturing treatment using the deformable pouches for fluid diversion between the treatment stages.

FIG. 5 depicts the laboratory setup to mimic a void in a formation and test its plugging by deformable pouches.

FIG. 6 shows the results obtained for the pressure drop across the plug formed during the experiment of Example 2.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to generally relates to using deformable pouches for wellbore operations. More specifically, embodiments of the present disclosure may relate to using deformable pouches for isolating perforated zones in cased and cemented wells during a multi-stage hydraulic fracturing treatment. During a multi-stage hydraulic fracturing treatment, zonal isolation may be required for diverting stimulating fluid away from certain perforated zones (e.g., already treated zones) so that the stimulating fluid may act upon and stimulate other perforated zones within the wellbore. Although some of the following discussion emphasizes diversion using deformable pouches in fracturing, a skilled artisan would readily recognize that the deformable pouches and methods of employing them described herein may be used prior to, during, or after many other wellbore operations (e.g., drilling, cementing, etc.). Some embodiments shall be described in terms of treatment of horizontal wells, but are equally applicable to wells of any orientation. Some embodiments shall be described for hydrocarbon production wells, but it is to be understood that they may be used for wells for production of other fluids, such as water or carbon dioxide, or, for example, for injection or storage wells.

In general, embodiments of the deformable pouches include an impermeable or moderately permeable shell (the pouch) enclosing a particulate filling material. The deformable pouches are included in a wellbore fluid which may then carry the deformable pouches downhole. The wellbore fluid that acts as a carrier fluid for the deformable pouches may be aqueous, oleaginous, or emulsions thereof—either of which may be optionally viscosified with a gelling agent. The size of the deformable pouches is a primary consideration for embodiments according to this disclosure and the overall size should be such that the deformable pouches are small enough, or in some instances deformable enough, to be able to pass through the perforations within the wellbore casing, but large enough to lodge into or plug the voids in the formation behind the casing, while not penetrating too deeply into the formation. In practice, two mechanisms may exist for the plugging of a void within the formation by the application of deformable pouches downhole: (1) the jamming of a void by a single pouch with a larger cross section than that of a point in the void (e.g., may jam at the throat or entrance of the void or may jam at a point further within the void); or (2) the formation of a bridge by the simultaneous arrival and agglomeration of multiple pouches within the void.

For example, FIG. 2 depicts a top-down sectional view of a wellbore illustrating the lodging/plugging that may occur after deformable pouches proceed past a perforation in the wellbore casing and accumulate in the void(s) of the formation. Specifically, FIG. 2 shows a formation 304 having a wellbore 312 formed therein. A casing 310 that lines wellbore 312 has a perforation 308 therein, exposing a void 302 (specifically a fracture in this embodiment) in the formation 304. A plug 300 comprised of a plurality of deformable pouches 306 forms within the void 302 in the formation 304 when the deformable pouches are small enough or deformable enough to pass through the perforation 308. While the illustrated embodiment shows the void as a fracture, it will be understood that in one or more embodiments, a void in the formation may include wormholes, perforation tunnels, hydraulic fractures, vugs, pores, or the like.

The deformability of the pouches renders the actual initial shape of the pouch somewhat irrelevant and in general, there are no limitations upon the shape of the deformable pouch as long as the deformable pouch is sized, shaped, and/or deformable enough to seal or plug a void from within the void (as opposed to on the wall of the wellbore). For example, and as the top-down sectional view of a wellbore shown in FIG. 2 depicts, once the deformable pouches 306 pass through the casing perforation and void opening 308 and encounter a restriction in the void space 302 of the formation 304, the pouches will be stressed and their shape will be deformed under the pressure imposed upon them by the wellbore fluid pushing the deformable pouches 306 against the formation 304 lodging them therein to form a plug 300. Indeed, the ability of the pouches to deform may actually facilitate the formation of a tighter seal or plug with a smaller volume of open space or open volume (e.g., smaller pores and lower permeability) in the formation voids than what can be achieved by a similar volume of rigid particulates that are not applied within the confines of a deformable pouch. In one or more embodiments, the permeability of the obtained seals or plugs in the voids may be from about 0.05-10 Darcy, or more specifically about 0.8 Darcy. This sealing effect may be likened to the ability of stacked sandbags to prevent the ingress of rising water due to the ability of the sandbags to deform under the pressure exerted by their stacking. Conveniently, methods using the deformable pouches may be capable of forming plugs that are adaptable to the size and shape heterogeneity of the voids encountered downhole and therefore may be successful in a wider variety of applications and/or in a smaller overall volume than particulates on their own (e.g., not enclosed in a pouch). Indeed, in some embodiments, a total bulk volume of deformable pouches, including their fluid and/or particulate content, needed for the isolation of a perforation cluster with 12 perforations may be as low as about 2 liters with a total weight of less than 1 kg. This is significantly less than for traditional free form particulate diverters such as rock salt or benzoic acid flakes which may require pumping over 25 kg of diverting material per perforated cluster.

In one or more embodiments, at least one dimension of the deformable pouches may be between about 1 mm and 100 mm. In more specific embodiments, at least one dimension of the deformable pouches may be between about 1 mm and 50 mm. In even more specific embodiments, at least one dimension of the deformable pouches may be between about 1 mm and 25 mm. In some embodiments, at least one dimension of the deformable pouches may be between about 1 mm and 10 mm. Further, the deformable pouches may possess at least two dimensions or each of its dimensions between one of the ranges presented above.

In one or more embodiments, the shell of the deformable pouches may be fabricated from a film or a fabric that is flexible and deformable, while also being impermeable or substantially impermeable to fluid flow therethrough. However, in one or more embodiments, the pouches may be moderately permeable. In some embodiments, the film or the fabric may be partially or completely destroyed in the downhole environment. For example, the film or fabric may be a material that is at least partially degradable, soluble, reactible, meltable or otherwise destroyable in the downhole environment as a result of the conditions inherent therein or as a result of the addition of a species (e.g., chemical reactant, pH modifier, etc.) to induce their destruction. Partial destruction of the film or fabric making up the deformable pouches may occur when at least 5%, or in some embodiments at least 50%, of the film or fabric is destroyed. Further, in some embodiments, the destruction of the deformable pouches may be engineered to occur over predetermined amount of time, thereby allowing the deformable pouches to be emplaced within voids of the formation intact prior to experiencing substantial destruction, or in some instances, any destruction. Some examples of dissolvable or degradable materials that may be used to create the deformable pouches include polylactic acid (PLA), polyesters and copolymers thereof, polyamides and copolymers thereof, polyglycolic acid, anhdyrides, polyethers and copolymers thereof, polyurethanes and the like.

Non-limiting examples of degradable materials that may be used include certain polymer materials that are capable of generating acids upon degradation. These polymer materials may herein be referred to as “polymeric acid precursors”; they can be used as destructible deformable pouch materials or as degradable diverting particulate materials, depending on their properties. These materials are typically solids at room temperature. The polymeric acid precursor materials include the polymers and oligomers that hydrolyze or degrade in certain chemical environments under known and controllable conditions of temperature, time, and pH to release organic acid molecules that may be referred to as “monomeric organic acids.” As used herein, the expression “monomeric organic acid” or “monomeric acid” may also include dimeric acid or acid with a small number of linked monomer units that function similarly to monomer acids composed of only one monomer unit, in that they are fully in solution at room temperature.

Polymer materials may include those polyesters obtained by polymerization of hydroxycarboxylic acids, such as the aliphatic polyesters of lactic acid, referred to as polylactic acid; of glycolic acid, referred to as polyglycolic acid; of 3-hydroxbutyric acid, referred to as polyhydroxybutyrate; of 2-hydroxyvaleric acid, referred to as polyhydroxyvalerate; of epsilon caprolactone, referred to as polyepsilon caprolactone or polycaprolactone; the polyesters obtained by esterification of hydroxyl amino acids such as serine, threonine and tyrosine; and the copolymers obtained by mixtures of the monomers listed above. A general structure for the above described homopolyesters is:

H—{O—[C(R1,R2)]_(x)—[C(R3,R4)]_(y)—C═O}_(z)—OH

Where R1, R2, R3, and R4 are either H, linear alkyl, such as CH3, CH₂CH₃ (CH₂)_(n)CH₃, branched alkyl, aryl, alkylaryl, a functional alkyl group (bearing carboxylic acid groups, amino groups, hydroxyl groups, thiol groups, or others) or a functional aryl group (bearing carboxylic acid groups, amino groups, hydroxyl groups, thiol groups, or others); x is an integer between 1 and 11; y is an integer between 0 and 10; and z is an integer between 2 and 50,000.

Under appropriate conditions (pH, temperature, water content) polyesters such as those described here may hydrolyze and degrade to yield hydroxycarboxylic acids and compounds such as those acids referred to in the foregoing as “monomeric acids.”

One example of a suitable degradable polymeric acid precursor, as mentioned above, is the polymer of lactic acid, sometimes called polylactic acid, “PLA,” polylactate or polylactide. Lactic acid is a chiral molecule and has two optical isomers. These are D-lactic acid and L-lactic acid. The poly(L-lactic acid) and poly(D-lactic acid) forms are generally crystalline in nature. Polymerization of a mixture of the L- and D-lactic acids to poly(DL-lactic acid) results in a polymer that is more amorphous in nature. In one or more embodiments, poly(L-lactic acid) and poly(D-lactic acid) may be used separately or may be used as a mixture of both optical isomers. The polymers described herein are essentially linear. The degree of polymerization of the linear polylactic acid can vary from as few units as necessary to make them solids under downhole conditions to several thousand monomeric units (e.g., 2000-5000). Cyclic structures may also be used. The degree of polymerization of these cyclic structures may be smaller than that of the linear polymers. These cyclic structures may include cyclic dimmers if they are solids under storage and wellsite ambient conditions.

Another example is the polymer of glycolic acid (hydroxyacetic acid), also known as polyglycolic acid (“PGA”), or polyglycolide. Other materials suitable as polymeric acid precursors (destructible deformable pouch materials or degradable diverting particulate materials, depending on their properties) are all those polymers of glycolic acid with itself or with other hydroxy-acid-containing moieties.

The polylactic acid and polyglycolic acid may each be used as homopolymers, which may contain less than about 0.1% by weight of other comonomers. As used with reference to polylactic acid, “homopolymer(s)” is meant to include polymers of D-lactic acid, L-lactic acid and/or mixtures or copolymers of pure D-lactic acid and pure L-lactic acid. Additionally, random copolymers of lactic acid and glycolic acid and block copolymers of polylactic acid and polyglycolic acid may be used. Combinations of the described homopolymers and/or the above-described copolymers may also be used.

Other examples of polyesters of hydroxycarboxylic acids that may be used as polymeric acid precursors are the polymers of hydroxyvaleric acid (polyhydroxyvalerate), hydroxybutyric acid (polyhydroxybutyrate) and their copolymers with other hydroxycarboxylic acids. Polyesters resulting from the ring opening polymerization of lactones such as epsilon caprolactone (polyepsiloncaprolactone) or copolymers of hydroxyacids and lactones may also be used as polymeric acid precursors.

Polyesters obtained by esterification of other hydroxyl-containing acid-containing monomers such as hydroxyamino acids may be used as polymeric acid precursors. Naturally occurring amino acids are L-amino acids. The three most common amino acids that contain hydroxyl groups are L-serine, L-threonine, and L-tyrosine. These amino acids may be polymerized to yield polyesters at the appropriate temperature and using appropriate catalysts by reaction of their alcohol and their carboxylic acid groups. D-amino acids are less common in nature, but their polymers and copolymers may also be used as polymeric acid precursors (destructible deformable pouch or degradable diverting particulate materials, depending upon properties). NatureWorks, LLC, Minnetonka, Minn., USA, produces solid cyclic lactic acid dimer called “lactide” and from it produces lactic acid polymers, or polylactates, with varying molecular weights and degrees of crystallinity, under the generic trade name NATUREWORKS™ PLA. The PLAs currently available from NatureWorks, LLC have number average molecular weights (M_(n)) of up to about 100,000 and weight averaged molecular weights (M_(w)) of up to about 200,000, although any polylactide (made by any process by any manufacturer) may be used. Those available from NatureWorks, LLC typically have crystalline melt temperatures of from about 120 to about 170° C., but others are obtainable. Poly(d,l-lactide) of various molecular weights is also commercially available from Bio-lnvigor, Beijing and Taiwan. Bio-lnvigor also supplies polyglycolic acid (also known as polyglycolide) and various copolymers of lactic acid and glycolic acid, often called “polygalactin” or poly(lactide-co-glycolide).

The extent of the crystallinity can be controlled by the manufacturing method for homopolymers and by the manufacturing method and the ratio and distribution of lactide and glycolide for the copolymers. Additionally, the chirality of the lactic acid used also affects the crystallinity of the polymer. Polyglycolide can be made in a porous form. Some of the polymers dissolve very slowly in water before they hydrolyze.

Amorphous polymers may be useful in certain applications. An example of a commercially available amorphous polymer is that available as NATUREWORKS 4060D PLA, available from NatureWorks, LLC, Which is a poly(DL lactic acid) and contains approximately 12% by Weight of D-lactic acid and has a number average molecular weight (M_(n)) of approximately 98,000 g/mol and a weight average molecular weight (M_(w)) of approximately 186,000 g/mol.

Other polymer materials that may be useful are the polyesters obtained by polymerization of polycarboxylic acid derivatives, such as dicarboxylic acid derivatives With polyhydroxy-containing compounds, in particular dihydroxy containing compounds. Polycarboxylic acid derivatives that may be used are those of dicarboxylic acids such as oxalic acid, propanedioic acid, malonic acid, fumaric acid, maleic acid, succinic acid, glutaric acid, pentanedioic acid, adipic acid, phthalic acid, isophthalic acid, terphthalic acid, aspartic acid, or glutamic acid; polycarboxylic acid derivatives are those such as of citric acid, poly and oligo acrylic acid and methacrylic acid copolymers; other materials that may be used if they are solids, or may be used as starting materials for polymerization if they are liquids, are dicarboxylic acid anhydrides, such as, maleic anhydride, succinic anhydride, pentanedioic acid anhydride, adipic acid anhydride, phthalic acid anhydride; dicarboxylic acid halides, primarily dicarboxylic acid chlorides, such as propanedioic acyl chloride, malonyl chloride, fumaroyl chloride, maleyl chloride, succinyl chloride, glutaroyl chloride, adipoyl chloride, and phthaloyl chloride. Useful polyhydroxy containing compounds for making useful degradable polymers are those dihydroxy compounds such as ethylene glycol, propylene glycol, 1,4butanediol, 1,5pentanediol, 1,6hexanediol, hydroquinone, resorcinol, bisphenols such as bisphenol acetone (bisphenol A) or bisphenol formaldehyde (bisphenol F); and polyols such as glycerol. When both a dicarboxylic acid derivative and a dihydroxy compound are used, a linear polyester results. It is understood that when one type of dicarboxylic acid is used, and one type of dihydroxy compound is used, a linear homopolyester is obtained. When multiple types of polycarboxylic acids and/or polyhydroxy containing monomers are used, copolyesters are obtained. According to the Flory Stockmayer kinetics, the “functionality” of the polycarboxylic acid monomers (number of acid groups per monomer molecule) and the “functionality” of the polyhydroxy containing monomers (number of hydroxyl groups per monomer molecule) and their respective concentrations, determine the configuration of the polymer (linear, branched, star, slightly crosslinked or fully crosslinked). All these configurations can be hydrolyzed or “degraded” to carboxylic acid monomers, and therefore can be considered as polymeric acid precursors (solids that can be used as destructible deformable pouch components or as degradable diverting particulate material components). As one non-limiting example, not descriptive all the possible polyester structures that can be used, but providing an indication of the general structure of the most simple cases encountered, the general structure for the linear homopolyesters useful is:

H—{O—R1-O—C═O—R2-C═O}_(z)—OH

Where R1 and R2 are linear alkyl, branched alkyl, aryl, and alkylaryl groups; and z is an integer between 2 and 50,000.

Other examples of suitable polymeric acid precursors are the polyesters derived from phthalic acid derivatives such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and the like.

Under the appropriate conditions (for example pH, temperature, and water content) polyesters such as those described herein can “hydrolyze” and “degrade” to yield polycarboxylic acids and polyhydroxy compounds, regardless of the original polyester synthesized from any of the polycarboxylic acid derivatives listed above. The polycarboxylic acid compounds yielded by the polymer degradation process are also considered monomeric acids.

Other examples of polymer materials that may be used are those obtained by the polymerization of sulfonic acid derivatives with polyhydroxy compounds, such as polysulphones or phosphoric acid derivatives with polyhydroxy compounds, such as polyphosphates.

Such solid polymeric acid precursor material may be capable of undergoing an irreversible breakdown into fundamental acid products downhole. As referred to herein, the term “irreversible” will be understood to mean that the solid polymeric acid precursor material, once broken downhole, does not reconstitute downhole, e.g., the material breaks down in situ but does not reconstitute in situ. The term “breakdown” refers to both of the two extreme cases of hydrolytic degradation that the solid polymeric acid precursor material may undergo, e.g., bulk erosion and surface erosion, and any stage of degradation in between these two. This degradation can be a result of, inter alia, a chemical reaction. The rate at which the chemical reaction takes place may depend on, inter alia, the chemicals added, temperature and time. The breakdown of solid polymeric acid precursor materials may or may not depend, at least in part, on their structure. For instance, the presence of hydrolyzable and/or oxidizable linkages in the backbone often yields a material that will breakdown as described herein. The rates at which such polymers breakdown are dependent on factors such as, but not limited to, the type of repetitive unit, composition, sequence, length, molecular geometry, molecular weight, morphology (e.g., crystallinity, size of spherulites, and orientation), hydrophilicity, hydrophobicity, surface area, and additives. The manner in which the polymer breaks down also may be affected by the environment to which the polymer is exposed, e. g., temperature, presence of moisture, oxygen, microorganisms, enzymes, pH, and the like.

Another class of suitable solid polymeric materials that may be used as destructible deformable pouches and/or degradable diversion particulate materials inside such pouches includes polyamides and polyimides. Such polymers may comprise hydrolyzable groups in the polymer backbone that may hydrolyze under the conditions that exist downhole. Non-limiting examples of suitable polyamides include proteins, polyamino acids, nylon, and poly(caprolactam). Another class of polymers that may be suitable for use is those polymers that may contain hydrolyzable groups, not in the polymer backbone, but as pendant groups. Hydrolysis of the pendant groups may generate a water soluble polymer and other byproducts. A non-limiting example of such a polymer is polyvinylacetate, which upon hydrolysis forms water-soluble polyvinylalcohol and acetate salts. Other suitable materials include polysaccharides, chitins, chitosans, orthoesters, polyanhydrides, polycarbonates, poly(orthoesters), poly(ethylene oxdides), and poly phosphazenes.

In other embodiments, the film or the fabric may be substantially stable and non-degradable under downhole conditions. In one or more embodiments, the film or fabric that is substantially stable and non-degradable under downhole conditions may be made from at least one of polyethylene, polyester, polyamide, polyethylene terephthalate, polysaccharides, cotton, wool, steel fabric, glass fabric, and asbestos fabric. Skilled artisans would understand that in order to keep films or fabric comprising polymeric materials substantially stable and non-degradable under downhole conditions, it may be useful to use those materials in specific conditions (e.g. certain temperatures and/or pH values). For example, in order to limit the hydrolysis and degradations of some of the polymers it may be useful to use them solely in situations where a downhole temperature will be below about 120° C. or in some embodiments below about 80° C. Further, in order to limit the hydrolysis and degradation of some of the polymers it may be useful to use them solely in situations where the downhole pH is from about 6-8.

The thickness and mechanical/chemical properties of the sheet, film or fabric used to make the deformable pouches may optionally be designed so that the premature destruction/degradation/dissolution is prevented or reduced during the pumping downhole and in the downhole conditions. In some embodiments, the thickness of the film or fabric that is formed into the deformable pouches may range from about 0.01 mm to about 5 mm, or from about 0.05 mm to about 2 mm, and potentially from about 0.1 mm to about 1 mm. Optionally, the deformable pouches may be made with several layers of film or fabric, for example up to about 10 layers, which may be the same or different material. The use of multiple layers may increase the mechanical stability of the deformable pouches and/or allow for better control of the dissolution time of the deformable pouch. Additionally, in some embodiments, the deformable pouch may include at least one pin hole fluidly connecting the outside of the pouch to the interior portion of the pouch. The at least one pin hole may serve to equalize the pressure between the inside of the pouches and wellbore during the pumping of the pouches downhole, thereby preventing or reducing their premature destruction due to differential pressure effects (e.g., by bursting or otherwise opening and emptying the contents therein).

The particulate materials enclosed within the deformable pouches may be described here in terms of solid diverting materials used in fracturing, but the deformable pouches may enclose any inert or reactive solids, fluids, or combinations of solids and fluids (e.g., a slurry) to any desired downhole location for any purpose, such as diversion, fluid loss control, etc. The deformable pouches are generally either a pre-formed pouch or bag that is then filled with particulate material or it may be a similarly structured pouch that is fashioned around the material to be contained (e.g., a shrinkable film enclosing the material); either way, it may be sealed or otherwise closed after it is filled with particulate or other material. The deformable pouch may be referred to as a shell, envelope, etc. In one or more embodiments, the particulate materials that are enclosed by the deformable pouches may be at least one of various fibers, flakes, platelets, ribbons, rods, precipitated material from chemical reactions, grains, pellets, spherical materials etc. Non-limiting examples of particulate materials that may be included within the deformable pouches include plastic beads, sand, ceramic beads, glass, wax beads, oil-soluble resins, benzoic acid flakes, cellophane flakes, crushed nut shells, crushed shells, ceramic proppant, silica flour, granulated polylactic acid (PLA), polyglycolic acid (PGA), rock salt, alumina, and calcium carbonate, polyethylene beads, glass beads, resin coated ceramic proppant including curable and procured resin coated ceramic, resin coated sand including curable and procured resin coated sand and mixtures thereof. The particulate materials enclosed within the deformable pouch may be of any size as long as they may be enclosed within the deformable pouch and may include mixtures of particulates of differing sizes and/or differing shapes (e.g., a mixture of spherical particles and fibers or flakes).

In some embodiments, the ability of the deformable pouches filled with particulate materials to conform to a variety of void size and shapes under the pressure applied by the wellbore fluid may facilitate the use of non-uniformly sized and shaped particulate materials. When enclosed within the deformable pouches, these solid particulate materials may effectively plug voids within a formation including, such as vugs, fluid loss pathways, hydraulic fractures, wormholes etc. In one or more embodiments, the solid particulate material may be degradable or otherwise destroyable under downhole conditions as described above for the film or fabric that makes up the deformable pouch. The use of degradable or otherwise destroyable particulates may facilitate the clearance of the plug or seal in the formation, which may be necessary in order for efficient production from the wellbore. Further, in some embodiments where the deformable pouches have pin holes, the film or fabric making up the deformable packages may be substantially stable under the downhole conditions while the particulate materials therein may be degradable or otherwise destroyable. In these instances, the degradation of the particulate materials within the stable deformable pouch may effectively loosen the seal or plug formed by the deformable pouches allowing for the clearance of the plug or seal in the formation without the destruction of the deformable pouch enclosure. In other embodiments, the solid particulate material may be substantially stable and maintain their seal indefinitely under downhole conditions, even if the film or fabric making up the deformable pouch is eventually destroyed under the downhole conditions. In some embodiments of deformable pouches, the use of a stable film or fabric and/or stable particulate material may be particularly useful for cementing or drilling applications where plug or seal removal is not completely necessary.

Indeed, in some embodiments, the shell of the deformable pouches may be specifically designed to be degradable downhole after forming a temporary seal in a void, while the particulate materials within the pouch remain stable and packed within the void to leave a highly permeable granulated filler within the void, allowing the voids to be open for production. For example, in a more specific embodiment, the shell of the deformable pouches may be made of degradable or otherwise destroyable materials and may be filled with non-degradable ceramic proppant. In this embodiment, the amount of degradable shell material that needs to degrade for increasing the conductivity within the temporarily sealed zone is much lower than the volume of the created plug or seal. However, in other embodiments, the shell and its particulate contents may be specifically designed to be degradable downhole after forming a temporary seal in a void, thereby increasing the conductivity of the near-wellbore zone.

The deformable pouches are intended to be introduced into a wellbore and pumped down to a target zone for sealing or plugging a void in the formation behind the wellbore casing. To introduce the deformable pouches into the fluid for pumping into the wellbore, a standard or modified flow injector, for example those used for ball sealers may be placed in the high pressure line. Such devices are typically used for injection of larger deformable pouches (those with a dimension greater than about 10 mm) and the injector is commonly installed after the pumping units so the deformable pouches are not subjected to forces that would break or damage them in the surface equipment. A schematic is shown in FIG. 3. Deformable pouches (not shown) are loaded into the accumulator 40 via a plug valve 42. The accumulator 40 is isolated from the main treating line 44 by two remotely operated valves 46. Then the plug valve 42 to the accumulator 40 is closed, the remotely operated valves 46 are opened and the deformable pouches are flushed from the accumulator 40 by the pumping fluid. A simple flow-through injection apparatus may also be used or the deformable pouches may be delivered downhole on bailers.

In one or more embodiments, before pumping the deformable pouches downhole, they may be pre-soaked in a fluid. This may be particularly useful when the deformable pouches are provided with pin holes that may allow the fluid to enter into the pouch and wet the particulate materials therein. In some embodiments, the pre-soaking may be used to initiate the dissolution/degradation processes of the film or fabric making up the deformable pouches and/or of the particulate materials therein. In some embodiments, the pre-soaking may be used to reduce the friction between the particulate materials enclosed within the deformable pouches. The reduction in friction accomplished by pre-soaking the deformable pouches may lead to a tighter packing of the pouches in the voids behind the wellbore casing and may also reduce the risk of the deformable pouches being destroyed during their pumping downhole.

For some applications, such as treatment diversion, deformable pouches may be used for setting temporary seals or plugs formed by the pouches and their contents. There are several mechanisms that may be used or occur during the removal of the seals formed: (1) self-degradation; (2) reaction with chemical agents; (3) melting at least one component of a deformable pouch or its contents; (4) dissolution of at least one component of the deformable pouches (i.e., the shell or the pouch contents); and (5) disintegration of at least one component of the deformable pouches (i.e., the shell or the pouch contents). These mechanisms will be explained below in further detail.

Self-degradation may occur when the shell and/or the particulate materials therein are unstable and degrade under the temperatures and conditions present downhole. Some examples of degradable materials are polyesters, including esters of lactic acid, glycolic acid, other hydroxy acids and copolymers thereof; polyamides and copolymers thereof; polyethers and copolymers thereof; polyurethanes, etc. Other examples of degradable materials which may encompass the film or fabric of the deformable pouches or their particulate contents were described above.

In some embodiments, an induced reaction with chemical agents may occur to chemically react with and thereby remove the seals or plugs formed by the deformable pouches and/or their particulate contents. In these instances, chemical agents may be pumped downhole after the treatment process that necessitated the sealing or plugging of the formation has completed with the express purpose of reacting with the deformable pouch and/or its particulate contents in order to clear the seal or plug. Some examples of materials that may be removed by reacting with other agents are carbonates including calcium and magnesium carbonates and mixtures thereof (reactive to acids and chelating agents); acid soluble cement (reactive to acids); polyesters including polyglycolic acid, polylactic acid, esters of lactic acid, glycolic acid, other hydroxyl acids, and copolymers thereof (can be hydrolyzed with acids and bases); active metals such as magnesium, aluminum, zinc and their alloys (reactive to water, acids and bases), etc.

In some embodiments, the melting of at least one component of the deformable pouch (i.e., the shell or pouch contents) may facilitate the removal of a plug or seal. When the shell or its contents contains a meltable component, its melting may results in a reduction of the mechanical stability of the plug, making it easier to be cleared. Examples of materials that may melt under downhole conditions include hydrocarbons having 30 or more carbon atoms; polycaprolactones; paraffins and waxes; carboxylic acids such as benzoic acid and its derivatives; etc.

In some embodiments, plug or seal removal may also be achieved through physical dissolution of at least one of the components of the deformable pouch (i.e., the shell and/or its particulate material contents) into the surrounding fluid. The solubility of the component(s) may depend significantly on the temperature. In this case, post-treatment temperature recovery in the sealed zone can trigger the removal of the seal. Materials that dissolve in water or water-based fluids may include water-soluble polymers, water-soluble elastomers, carbonic acids, rock salt, amines, and inorganic salts. Materials that may dissolve in oil or oil-based fluids may include oil-soluble polymers, oil-soluble resins, oil-soluble elastomers, polyethylene, carbonic acids, amines, and waxes.

In some embodiments, plug or seal removal may be achieved through the disintegration of the shell or its particulate material contents into smaller pieces that may be more readily flushed away. Materials that can disintegrate include plastics such as PLA, polyamides and composite materials comprising degradable plastics and non-degradable fine solids. It should be noted that some degradable materials pass through a disintegration stage during the degradation process. An example is PLA, which turns into a fragile material before complete degradation.

FIG. 4 depicts a flow chart 500 for a multi-stage hydraulic fracturing treatment using the deformable pouches for fluid diversion between the treatment stages. In 502, the multi-stage treatment is initiated by perforating the wellbore casing to form a perforation cluster. During the perforation the wellbore casing is perforated and perforation tunnels (formation voids) may be formed a depth into the formation. In 504, the perforation cluster is subjected to a fracturing treatment. In 506, a calculated amount of deformable pouches are pumped downhole for sealing the treated zone. In 508, the deformable pouches are injected into the perforation cluster and seal it. In 510, after the plugs or seals are formed in the treated zone in 508, the perforation gun is moved for perforating a new zone of the wellbore. The stages may then repeat for treating other wellbore zones until the desired number of a plurality of wellbore zones are treated. Further, if no increase in wellbore pressure is observed after injection of the deformable pouches, then a plug might not have been formed by the deformable pouches, and it may be desirable to repeat pumping of another volume of the pouches or use a different method of diversion and/or isolation to form a sufficient plug.

The delivery of solid particulate materials downhole in the form of deformable pouches may allow for the use of significantly less solid particulate materials to accomplish a diversion or to form a plug or seal than by simply adding the particulate materials to the fluid itself. This is due to the conventional downhole dilution of the particulate materials being eliminated by their confinement in the deformable pouch. Further, the use of less amounts of solid particulate materials downhole reduces the risk of wellbore plugging during diversion stages or other treatments. Additionally, not only would using a lower amount of solid particulate materials downhole save money, it may also reduce the risk of formation damage from the application of large amounts of materials downhole, while also enabling more efficient post-treatment clean-up as a negligible amount of particulate material would likely remain in the wellbore, thereby eliminating additional wellbore cleaning that is commonly required after the application of materials downhole.

EXAMPLES Example 1

To demonstrate that deformable pouches can form a plug or seal with low permeability 20 mm×10 mm deformable pouches (a shell of polyethylene film filled with polylactic acid particulates) were utilized in a test using the setup shown in FIG. 5 to mimic a void in a formation. The setup includes a tube 80, which serves as an accumulator for a plug. There is a 6 mm slot 82 on one end and a pump providing for fluid flow 84 on the other end. Before the experiment the accumulator was filled with deformable pouches suspended within a 0.5% guar gum solution. Then the contents of the accumulator was displaced into the slot with water at a pumping rate of 1 L/min. The permeability of the formed plug resulting from the deformable pouches blocking the slot was calculated based upon the pressure drop across the plug of about 400 psi, with the obtained value equaling about 0.8 Darcy. FIG. 6 shows the results obtained for the pressure drop across the plug.

While the use of deformable pouches enclosing solid particulate materials for sealing or plugging voids in a formation behind a wellbore casing has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 

What is claimed:
 1. A method for plugging or sealing voids in a formation, comprising: introducing deformable pouches enclosing solid particulate materials into a fluid being pumped down the well; and injecting the deformable pouches into the voids of the formation; wherein at least one dimension of the deformable pouches may be between about 1 mm and 100 mm.
 2. The method of claim 1, wherein a shell of the deformable pouches are made of a film or fabric that is partially or completely destroyed in the downhole environment.
 3. The method of claim 2, wherein the film or fabric is at least partially degradable, soluble, reactible, or meltable in the downhole environment.
 4. The method of claim 2, wherein the film or fabric include at least one of polylactic acid, polyesters, polyamides, polyglycolic acid, polyurethanes, polyethers, anhdyrides, and copolymers thereof.
 5. The method of claim 2, wherein the thickness of the film or fabric ranges from about 0.01 mm to about 5 mm.
 6. The method of claim 1, wherein the deformable pouches include at least one pin hole fluidly connecting the outside of the pouch to the interior portion of the pouch.
 7. The method of claim 1, wherein the solid particulate materials enclosed by the deformable pouches includes at least one of fibers, flakes, platelets, ribbons, rods, precipitated material from chemical reactions, grains, pellets, spherical materials.
 8. The method of claim 1, wherein the solid particulate materials enclosed by the deformable pouches includes at least one of plastic beads, sand, ceramic beads, glass, wax beads, oil-soluble resins, benzoic acid flakes, cellophane flakes, crushed nut shells, crushed shells, ceramic proppant, silica flour, granulated polylactic acid (PLA), polyglycolic acid (PGA), rock salt, alumina, and calcium carbonate, polyethylene beads, glass beads, resin coated ceramic proppant including curable and procured resin coated ceramic, resin coated sand including curable and procured resin coated sand.
 9. The method of claim 1, wherein the solid particulate material enclosed by the deformable pouches is partially or completely destroyed in the downhole environment.
 10. The method of claim 1, wherein the solid particulate material enclosed by the deformable pouches is substantially stable in the downhole environment.
 11. The method of claim 1, wherein at least one dimension of the deformable pouches is between about 1 mm and 50 mm.
 12. The method of claim 1, wherein at least one dimension of the deformable pouches is between about 1 mm and 25 mm.
 13. The method of claim 1, wherein at least one dimension of the deformable pouches is between about 1 mm and 10 mm.
 14. The method of claim, further comprising: pre-soaking the deformable pouches in a fluid prior to the introducing.
 15. A method for fracturing a wellbore, comprising: perforating a wellbore casing to form a perforation cluster in a first zone of a wellbore casing; subjecting the perforation cluster in the first zone to a fracturing treatment; pumping a fluid including deformable pouches downhole; and injecting the deformable pouches into voids in the formation behind the first zone of the wellbore casing.
 16. The method for fracturing a wellbore of claim 15, further comprising: repeating the perforating the wellbore casing to form a perforation cluster in a wellbore casing, subjecting the formed perforation cluster to a fracturing treatment, pumping a fluid including deformable pouches downhole, and injecting the deformable pouches into voids in the formation until a plurality of zones in the wellbore casing are fractured.
 17. The method of claim 15, wherein a shell of the deformable pouches are made of a film or fabric that is partially or completely destroyed in the downhole environment.
 18. A method for plugging or sealing voids in a formation, comprising: introducing deformable pouches enclosing solid particulate materials into a fluid being pumped down the well; and injecting the deformable pouches into the voids of the formation located behind the wellbore casing; wherein at least one dimension of the deformable pouches may be between about 1 mm and 100 mm; and wherein the deformable pouches are partially or completely destroyable in the downhole environment.
 19. A method for plugging or sealing voids in a formation, comprising: introducing deformable pouches enclosing solid particulate materials into a fluid being pumped down the well; and packing the deformable pouches into the voids of the formation; wherein at least one dimension of the deformable pouches may be between about 1 mm and 100 mm; and wherein the deformable pouches are substantially stable in the downhole environment.
 20. The method of claim 19, wherein the plugging or sealing voids in a formation occurs during a drilling or cementing process. 